This invention relates to stoves or furnaces used as heating units, and specifically, to stoves provided with a catalytic converter for treating the effluent gases produced by combustion.
With the energy crises and the increase in expense of fuel, people have become preoccupied in maximizing the use of inexpensive fuels. One particularly available, inexpensive and replenishable fuel is wood and wood by-products. Increasingly, this source of fuel has been taken advantage of by the use of wood burning stoves and furnaces to employ the heat release by combustion as a supplement or replacement for conventional domestic and small commercial heating systems.
Generally, the heat is transferred to the room by radiation from the surface of the stove wall or, more practically, through a forced air system, employing one or more channels surrounding the walls of the stove as a heat exchange means. A stove of the latter type is disclosed in Buckner et al. U.S. Pat. No. 4,301,783.
The combustion of wood and similar fuels produces effluent gases rich in creosote and similar hydrocarbon pollutants, which are potentially harmful when released to the atmosphere. The same pollutants present serious dangers of chimney and house fires when deposited on the walls of flues and chimneys as the effluent gases pass therethrough. The use of wood burning stoves has grown so prevalent in many states that governmental authorities are taking steps to require that all such heating units be provided with effluent gas treatment means for controlling the level of pollutants that are expelled. In any event, even in the absence of such legislation, keeping pollution to a minimum is an obviously desirable goal.
The use of a catalytic converter as an effluent gas treatment means is becoming increasingly common in wood stoves. Patents disclosing such usage include U.S. Pat. Nos. 4,319,556 and 4,373,507. However, the use of a catalytic converter in a wood stove is not a simple matter and a considerable number of obstacles must be overcome for the converter to work properly.
As illustrated in U.S. Pat. Nos. 4,319,556 and 4,373,507, the catalyst is conventionally placed directly over the combustion site of the heating stove. When the flames of the fire grow to a maximum, the problem of flame impingement directly on the catalyst may severely reduce the effective life and efficiency of the catalytic converter. At the same time, location of the catalytic converter in direct communication with the combustion site results in a substantial amount of particulate matters, largely ash, being deposited upon the catalytic surface of the converter, again severely decreasing both the life and efficiency of the catalytic converter.
The presence of the catalytic converter, combined with the need to replenish the fuel supply, has also presented problems when using the existing systems. Generally, to replenish the fuel supply, a door opening on the combustion site is opened and the solid fuel added to the combustion site. Of course, the effluent gas is constantly being generated, even while fuel is being added to the fire. The presence of a catalytic converter creates a substantial back pressure, such that, when the door to the combustion site is opened, the produced smoke tends to escape into the room being heated, which is substantial annoyance and a safety hazard.
At the same time, the opening of the door allows the relatively cooler air of the surrounding areas to rush into the combustion site area. In conventional systems, the catalytic converter is in direct communication with this area and the colder room air impacts directly on the converter surface. This substantially drops the temperature of the converter to a point where it is no longer operative rendering the converter substantially useless until the heat from the fire reheats the converter. During this time, which is generally quite longer than the time necessary to add fuel to the fire, any effluent gas passing through the converter will be to the air pollution.
To avoid the aforementioned problems, it has been proposed to locate the catalytic converter away from direct contact with the combustion site. In U.S. Pat. No. 4,345,528, there is disclosed the placement of the converter in the flue of the stove. However, it has been found that the remote placement of the catalytic converter can cause oxygen starvation in the converter thereby reducing the converter's efficiency. The remote placement of the converter also presents problems in removing the catalytic converter for service and/or replacement.
Thus, there exists a need for a wood burning stove with a catalytic converter that can overcome all of the aforementioned problems and also provide sufficient oxygen flow to the converter.
Accordingly, it is one object of this invention to provide a catalytic converter apparatus for solid fuel stoves which will overcome all of the above-described problems.
It is another object of this invention to provide a catalytic converter apparatus which is not subject to flame impingement and is not cooled when the stove door is opened.
It is another object of this invention to provide a catalytic converter apparatus which is not subjected to the deposition of particulate matters on its catalytic surfaces.
Still another object of this invention is to provide an a catalytic converter apparatus which does not cause smoke to fill the room to be heated when the stove door is opened.
Yet another object of this invention is to provide a supplemental air flow to the catalytic converter to allow the converter to operate at peak efficiency.
Still another object of this invention is to provide a catalytic converter apparatus in which the catalytic elements can be readily replaced.
It is still yet another object of this invention to provide a solid fuel stove useful as a heater which includes an effluent gas treatment apparatus enjoying all of the above-described advantages.